DEFINE ‘THOROUGH’…. The evidence pointing to a weak and cursory vetting process in the McCain campaign is pretty overwhelming, but John McCain doesn’t want us to believe a word of it.

“The vetting process was completely thorough, and I’m grateful for the results,” McCain said during a campaign stop this morning at Engine Company 56 of the Philadephia Fire Department.

His aides have said nothing has emerged in news reports about Palin that McCain and the campaign did not know before selecting her, including that her 17-year-old daughter Bristol was pregnant.

Look, McCain is in a bind, and the truth is, there is no compelling response. If McCain says he oversaw a thorough vetting process, that means he knew all about all of the various Palin controversies — the abuse of power, the lobbying for pork projects, the affiliation with the fringe secessionist party, etc. — and nevertheless concluded, after having spent 15 minutes chatting with her six months ago, she should be one heartbeat from the presidency.

If McCain concedes the vetting process was incomplete, that means he failed in the most important task of his presidential campaign, flubbing the key test of every major party nominee.

In other words, if McCain says there was a thorough vetting, he ends up looking like a fool. If he acknowledges there wasn’t a through vetting, he ends up looking like a fool.

It’s an unpleasant situation for a candidate to find himself in, isn’t it?

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.